High-speed sampler

ABSTRACT

A regeneration circuit includes a first inverting circuit and a second inverting circuit. The regeneration circuit also includes a first transistor coupled to an input of the second inverting circuit, and a second transistor coupled to an input of the first inverting circuit, a third transistor and a fourth transistor. A gate of the first transistor and a gate of the fourth transistor are coupled to a first input, and a gate of the second transistor and a gate of the fourth transistor are coupled to a second input. The regeneration circuit further includes a first switch and a second switch. The first switch and the third transistor are coupled in series between a first rail and the first transistor, and the second switch and the fourth transistor are coupled in series between the first rail and the second transistor.

BACKGROUND Field

Aspects of the present disclosure relate generally to samplers, and moreparticularly, to high-speed samplers.

Background

High-speed samplers may be used in high-speed serializer/deserializer(SerDes) applications. For example, a sampler may be used in high-speedSerDes to sample a high-speed signal received by a receiver. The samplermay include a regeneration circuit that provides the sampler withregenerative feedback for quickly capturing data bits from the receivedsignal. It is desirable to increase the speed of the sampler to sample asignal at higher data rates and/or increase the sensitivity of thesampler to capture data bits from a small signal.

SUMMARY

The following presents a simplified summary of one or moreimplementations in order to provide a basic understanding of suchimplementations. This summary is not an extensive overview of allcontemplated implementations and is intended to neither identify key orcritical elements of all implementations nor delineate the scope of anyor all implementations. Its sole purpose is to present some concepts ofone or more implementations in a simplified form as a prelude to themore detailed description that is presented later.

A first aspect relates to a regeneration circuit. The regenerationcircuit includes a first inverting circuit having an input and anoutput, and a second inverting circuit having an input and an output.The regeneration circuit also includes a first transistor coupled to theinput of the second inverting circuit, wherein a gate of the firsttransistor is coupled to a first input, and a second transistor coupledto the input of the first inverting circuit, wherein a gate of thesecond transistor is coupled to a second input. The regeneration circuitfurther includes a third transistor, wherein a gate of the thirdtransistor is coupled to the first input, and a fourth transistor,wherein a gate of the fourth transistor is coupled to the second input.The regeneration circuit further includes a first switch, wherein thefirst switch and the third transistor are coupled in series between afirst rail and the first transistor, and a second switch, wherein thesecond switch and the fourth transistor are coupled in series betweenthe first rail and the second transistor.

A second aspect relates to a regeneration circuit. The regenerationcircuit includes a first inverting circuit having an input and anoutput, a second inverting circuit having an input and an output, afirst transistor coupled to the input of the second inverting circuit,wherein a gate of the first transistor is coupled to a first input, anda second transistor coupled to the input of the first inverting circuit,wherein a gate of the second transistor is coupled to a second input.The regeneration circuit also includes a pull-up circuit coupled to theinput of the first inverting circuit and the input of the secondinverting circuit, and a pull-down circuit coupled to the input of thefirst inverting circuit and the input of the second inverting circuit.

A third aspect relates to a method of operating a regeneration circuitof a sampler. The regeneration circuit includes a first invertingcircuit having an input and an output, a second inverting circuit havingan input and an output, a first transistor coupled to the input of thesecond inverting circuit, a second transistor coupled to the input ofthe first inverting circuit, a third transistor, and a fourthtransistor. The method includes, during a reset phase, disabling aregenerative feedback of the first inverting circuit and the secondinverting circuit. The method also includes, during a regenerationphase, enabling the regenerative feedback of the first inverting circuitand the second inverting circuit. driving a gate of the first transistorand a gate of the third transistor with a first voltage, driving a gateof the second transistor and a gate of the fourth transistor with asecond voltage, and coupling the third transistor to the output of thefirst inverting circuit or coupling the fourth transistor to the outputof the second inverting circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a sampler including an input circuit and aregeneration circuit according to certain aspects of the presentdisclosure.

FIG. 2A shows an exemplary implementation of the input circuit accordingto certain aspects of the present disclosure.

FIG. 2B shows an exemplary implementation of the regeneration circuitaccording to certain aspects of the present disclosure.

FIG. 2C shows another exemplary implementation of the regenerationcircuit according to certain aspects of the present disclosure.

FIG. 3A is a timing diagram showing an example of voltages output by theinput circuit to the regeneration circuit according to certain aspectsof the present disclosure.

FIG. 3B is a timing diagram showing another example of voltages outputby the input circuit to the regeneration circuit according to certainaspects of the present disclosure.

FIG. 4 shows an example of the regeneration circuit including a pull-upcircuit according to certain aspects of the present disclosure.

FIG. 5A shows an example of the regeneration circuit including apull-down circuit according to certain aspects of the presentdisclosure.

FIG. 5B shows another example of the regeneration circuit including apull-down circuit according to certain aspects of the presentdisclosure.

FIG. 6 shows an example of the regeneration circuit including inputtransistors providing a pull-up path according to certain aspects of thepresent disclosure.

FIG. 7 shows an exemplary implementation of the input transistorsaccording to certain aspects of the present disclosure.

FIG. 8 shows an exemplary implementation of switches in the regenerationcircuit according to certain aspects of the present disclosure.

FIG. 9A shows an exemplary implementation of a first inverting circuitin the regeneration circuit according to certain aspects of the presentdisclosure.

FIG. 9B shows an exemplary implementation of a second inverting circuitin the regeneration circuit according to certain aspects of the presentdisclosure.

FIG. 10 shows an exemplary implementation of switches in the inputcircuit according to certain aspects of the present disclosure.

FIG. 11 shows an example of a system in which aspects of the presentdisclosure may be used according to certain aspects of the presentdisclosure.

FIG. 12 is a flowchart illustrating an exemplary method of operating aregeneration circuit according to certain aspects of the presentdisclosure.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with theappended drawings, is intended as a description of variousconfigurations and is not intended to represent the only configurationsin which the concepts described herein may be practiced. The detaileddescription includes specific details for the purpose of providing athorough understanding of the various concepts. However, it will beapparent to those skilled in the art that these concepts may bepracticed without these specific details. In some instances, well-knownstructures and components are shown in block diagram form in order toavoid obscuring such concepts.

FIG. 1 shows an example of a sampler 110 according to certain aspects ofthe present disclosure. The sampler 110 may be used, for example, inhigh-speed SerDes to sample an incoming data signal. The sampler 110 mayalso be referred to as a sense amplifier or another term. The sampler110 includes an input circuit 120 and a regeneration circuit 150. Theinput circuit 120 may also be referred to as an input stage or anotherterm, and the regeneration circuit 150 may also be referred to as aregeneration stage, a latch (e.g., cross-coupled latch), or anotherterm.

As shown in FIG. 1 , the input circuit 120 has a first input 130, asecond input 135, a first output 140, and a second output 145. Theregeneration circuit 150 has a first input 160, a second input 165, afirst output 170, and a second output 175. The first input 160 of theregeneration circuit 150 is coupled to the first output 140 of the inputcircuit 120, and the second input 165 of the regeneration circuit 150 iscoupled to the second output 145 of the input circuit 120.

In this example, the input circuit 120 is configured to receive adifferential input signal (e.g., differential data signal) that includesa first input voltage INP and a second input voltage INN. The firstinput voltage INP is received at the first input 130 and the secondinput voltage INN is received at the second input 135. The differentialinput signal may have a small differential voltage (i.e., a smalldifference between the first input voltage INP and the second inputvoltage INN) in which the polarity of the differential voltagerepresents a bit value. For the example of SerDes, the sampler 110 maybe integrated on a first chip that is coupled to a second chip via alink, and the sampler may receive the differential input signal from atransmitter on the second chip via the link.

The input circuit 120 generates a first voltage DINT at the first output140 and a second voltage NDINT at the second output 145 based on thefirst input voltage INP and the second input voltage INN. As discussedfurther below, the input circuit 120 is configured to set the firstvoltage DINT and the second voltage NDINT to a reset voltage (e.g.,supply voltage) during a reset phase, and change (e.g., discharge) thefirst voltage DINT and the second voltage NDINT at different rates basedon the first input voltage INP and the second input voltage INN during aregeneration phase.

The regeneration circuit 150 is configured to receive the first voltageDINT at the first input 160 and receive the second voltage NDINT at thesecond input 165. As discussed further below, during the regenerationphase, the regeneration circuit 150 is configured to convert the firstvoltage DINT and the second voltage NDINT into a differential outputvoltage using regenerative feedback. The differential output signalincludes a first output voltage OUTP at the first output 170 and asecond output voltage OUTN at the second output 175, in which thepolarity of the differential output voltage represents a captured (i.e.,resolved) bit value. It is desirable for the regeneration circuit 150 toquickly convert the first voltage DINT and the second voltage NDINT intoa large differential output voltage (i.e., a large difference betweenthe first output voltage OUTP and the second output voltage OUTN) duringthe regeneration phase to quickly resolve a bit value for high-speedapplications.

The first output 170 and the second output 175 of the regenerationcircuit 150 may be coupled to a latch (not shown) configured to latch acaptured bit value from the sampler 110. The latch may include aset-reset (SR) latch or another type of latch.

FIG. 2A shows an exemplary implementation of the input circuit 120according to certain aspects. The input circuit 120 includes a firstinput transistor 210, a second input transistor 220, a first switch 230,a second switch 240, and a third switch 245. The second switch 240 iscoupled between an upper rail 280 and the first input transistor 210,and the third switch 245 is coupled between the upper rail 280 and thesecond input transistor 220. The first input transistor 210 is coupledbetween the second switch 240 and node 226, and the second inputtransistor 220 is coupled between the third switch 245 and node 226. Thefirst switch 230 is coupled between node 226 and a lower rail 285. Inone example, the upper rail 280 may provide a supply voltage VCC and thelower rail 285 may be coupled to ground. In general, the upper rail 280is at a higher potential than the lower rail 285. The upper rail 280 mayalso be referred to as a supply rail or another term.

In the example shown in FIG. 2A, the first input transistor 210 isimplemented with a first n-type field effect transistor (NFET) and thesecond input transistor 220 is implemented with a second NFET. It is tobe appreciated that the first input transistor 210 and the second inputtransistor 220 are not limited to NFETs and may be implemented withother types of transistors. In this example, the second switch 240 iscoupled between the upper rail 280 and the drain of the first inputtransistor 210, and the first switch 230 is coupled between the sourceof the first input transistor 210 and the lower rail 285. The gate ofthe first input transistor 210 is coupled to the first input 130 of theinput circuit 120 and therefore receives the first input voltage INP.Also, in this example, the third switch 245 is coupled between the upperrail 280 and the drain of the second input transistor 220, and the firstswitch 230 is coupled between the source of the second input transistor220 and the lower rail 285. The gate of the second input transistor 220is coupled to the second input 135 of the input circuit 120 andtherefore receives the second input voltage INN.

The first switch 230 has a control input 235 driven by a timing signal,the second switch 240 has a control input 242 driven by the timingsignal, and the third switch 245 has a control input 247 driven by thetiming signal. In one example, the first switch 230 is configured toturn on when the timing signal is high and turn off when the timingsignal is low, and each one of the second switch 240 and the thirdswitch 245 is configured to turn on when the timing signal is low andturn off when the timing signal is high. In the example shown in FIG.2A, the timing signal is a clock signal CLK. As used herein, a “clocksignal” is a periodic signal that oscillates between a high logic stateand a low logic state. In certain aspects, a high logic state (i.e.,logic state of one) may correspond to a voltage approximately equal tothe supply voltage VCC and a low logic state (i.e., logic state of zero)may correspond to a voltage approximately equal to ground.

As used herein, a “control input” of a switch is an input that controlsthe on/off state of the switch based on a signal (e.g., a voltagesignal) at the control input. For an example where a switch isimplemented with a transistor, the control input is located at the gateof the transistor. In one example, the first switch 230 may beimplemented with an NFET, and each of the second switch 240 and thethird switch 245 may be implemented with a respective PFET. However, itis to be appreciated that the present disclosure is not limited to thisexample.

In this example, the first output 140 is coupled to a first node 222between the second switch 240 and the first input transistor 210, andthe second output 145 is coupled to a second node 224 between the thirdswitch 245 and the second input transistor 220. As discussed above, theinput circuit 120 outputs the first voltage DINT at the first output 140and outputs the second voltage NDINT at the second output 145. In theexample in FIG. 1 , the first output 140 is coupled to the drain of thefirst input transistor 210, and the second output 145 is coupled to thedrain of the second input transistor 220.

FIG. 2B shows an exemplary implementation of the regeneration circuit150 according to certain aspects. In this example, the regenerationcircuit 150 includes a first input transistor 250, a second inputtransistor 255, a first switch 290, a second switch 295, a firstinverting circuit 260, and a second inverting circuit 270. As discussedfurther below, the first inverting circuit 260 and the second invertingcircuit 270 are cross coupled during the regeneration phase to provideregenerative feedback. As used herein, an “inverting circuit” is acircuit configured to invert a logic state (i.e., logic level or logicvalue) at an input of the inverting circuit and output the invertedlogic state at an output of the inverting circuit. The logic state maybe represented by a voltage in which a low voltage (e.g., approximatelyground) may represent a logic state of zero and a high voltage (e.g.,approximately a supply voltage) may represent a logic state of one. Incertain aspects, an inverting circuit has a threshold voltage in whichthe output of the inverting circuit transitions from low to high whenthe voltage at the input of the inverting circuit falls below thethreshold voltage, and the output of the inverting circuit transitionsfrom high to low when the voltage at the input of the inverting circuitrises above the threshold voltage. An inverting circuit may also bereferred to as an inverter, an inverting circuit, or another term.

The first inverting circuit 260 has an input 262, an output 264, a firstsupply terminal 266, and a second supply terminal 268. The secondinverting circuit 270 has an input 272, an output 274, a first supplyterminal 276, and a second supply terminal 278. The first supplyterminal 266 of the first inverting circuit 260 and the first supplyterminal 276 of the second inverting circuit 270 are coupled to theupper rail 280. The second supply terminal 268 of the first invertingcircuit 260 and the second supply terminal 278 of the second invertingcircuit 270 are coupled to the lower rail 285 (e.g., ground).

The first switch 290 is coupled between the input 272 of the secondinverting circuit 270 and the output 264 of the first inverting circuit260, and the second switch 295 is coupled between the input 262 of thefirst inverting circuit 260 and the output 274 of the second invertingcircuit 270. When the first switch 290 and the second switch 295 areturned on, the first inverting circuit 260 and the second invertingcircuit 270 are crossed coupled, in which the input 272 of the secondinverting circuit 270 is coupled to the output 264 of the firstinverting circuit 260 through the first switch 290, and the input 262 ofthe first inverting circuit 260 is coupled to the output 274 of thesecond inverting circuit 270 through the second switch 295. As discussedfurther below, the first switch 290 and the second switch 295 are turnedon during the regeneration phase to enable regenerative feedback of thefirst inverting circuit 260 and the second inverting circuit 270, andthe first switch 290 and the second switch 295 are turned off during thereset phase to disable regenerative feedback of the first invertingcircuit 260 and the second inverting circuit 270. Each of the firstswitch 290 and the second switch 295 may be implemented with arespective transistor (e.g., respective NFET), a respective transmissiongate, or another type of switch.

The first input transistor 250 is coupled between the input 272 of thesecond inverting circuit 270 and the lower rail 285. The gate of thefirst input transistor 250 is coupled to the first input 160 of theregeneration circuit 150. Thus, the gate of the first input transistor250 is configured to receive the first voltage DINT (i.e., the firstinput signal to the regeneration circuit 150). In one example, the firstinput transistor 250 is configured to turn on when the voltage DINT isabove a threshold voltage of the first input transistor 250 and turn offwhen the voltage DINT is below the threshold voltage of the first inputtransistor 250. In the example shown in FIG. 2B, the first inputtransistor 250 is implemented with an NFET, in which the drain of thefirst input transistor 250 is coupled to the input 272 of the secondinverting circuit 270 and the source of the first input transistor 250is coupled to the lower rail 285. Also, the first switch 290 is coupledbetween the output 264 of the first inverting circuit 260 and the drainof the first input transistor 250. It is to be appreciated that thefirst input transistor 250 may also be implemented with another type oftransistor. In this example, the first output 170 is coupled to theoutput 264 of the first inverting circuit 260.

The second input transistor 255 is coupled between the input 262 of thefirst inverting circuit 260 and the lower rail 285. The gate of thesecond input transistor 255 is coupled to the second input 165 of theregeneration circuit 150. Thus, the gate of the second input transistor255 is configured to receive the second voltage NDINT (i.e., the secondinput signal to the regeneration circuit 150). In one example, thesecond input transistor 255 is configured to turn on when the voltageNDINT is above a threshold voltage of the second input transistor 255and turn off when the voltage NDINT is below the threshold voltage ofthe second input transistor 255. In the example shown in FIG. 2B, thesecond input transistor 255 is implemented with an NFET, in which thedrain of the second input transistor 255 is coupled to the input 262 ofthe first inverting circuit 260 and the source of the second inputtransistor 255 is coupled to the lower rail 285. Also, the second switch295 is coupled between the output 274 of the second inverting circuit270 and the drain of the second input transistor 255. It is to beappreciated that the second input transistor 255 may also be implementedwith another type of transistor. In this example, the second output 175is coupled to the output 274 of the second inverting circuit 270.

In the example in FIG. 2B, the first switch 290 has a control input 292driven by the timing signal, and the second switch 295 has a controlinput 297 driven by the timing signal (e.g., the clock signal CLK). Inone example, the first switch 290 and the second switch 295 areconfigured to turn on when the timing signal is high and turn off whenthe timing signal is low. Thus, in this example, the first switch 290and the second switch 295 turn on when the first switch 230 in the inputcircuit 120 turns on, and the first switch 290 and the second switch 295turn off when the second switch 240 and the third switches 245 in theinput circuit 120 turn on. For the example where each of the firstswitch 290 and the second switch 295 is implemented with a respectivetransistor, the control input 292 and 297 of each of the first switch290 and the second switch 295 is located at the gate of the respectivetransistor. In one example, each of the first switch 290 and the secondswitch 295 may be implemented with a respective NFET.

Exemplary operations of the sampler 110 will now be discussed accordingto certain aspects.

When the timing signal (e.g., the clock signal CLK) is low, the sampler110 is in the reset phase. In the reset phase, the first switch 230 inthe input circuit 120 is turned off. As a result, the first switch 230decouples the first input transistor 210 and the second input transistor220 of the input circuit 120 from the lower rail 285 (e.g., ground). Thesecond switch 240 and the third switch 245 are turned on. As a result,the second switch 240 couples the first output 140 to the upper rail 280and the third switch 245 couples the second output 145 to the upper rail280. This causes the input circuit 120 to pull up the first output 140and the second output 145 to the supply voltage VCC on the upper rail280. Thus, the first voltage DINT input to the gate of the first inputtransistor 250 of the regeneration circuit 150 and the second voltageNDINT input to the gate of the second input transistor 255 of theregeneration circuit 150 are both pulled up to VCC during the resetphase.

Also, in the reset phase, the first switch 290 and the second switch 295in the regeneration circuit 150 are turned off. As a result, theregeneration feedback in the regeneration circuit 150 is disabled (i.e.,the cross-coupling of the inverting circuits 260 and 270 is broken). Inaddition, the first input transistor 250 and the second input transistor255 of the regeneration circuit 150 are both turned on since the voltageDINT and the voltage NDINT are both pulled up to the supply voltage VCC(assuming VCC is greater than the threshold voltage of the first inputtransistor 250 and the threshold voltage of the second input transistor255). As a result, the inputs 262 and 272 of the inverting circuits 260and 270 are pulled low (e.g., ground). This causes the outputs 264 and274 of the inverting circuits 260 and 270 to be pulled high. In thisexample, the first output 170 and the second output 175 of theregeneration circuit 150 are also pulled high.

When the timing signal (e.g., the clock signal CLK) transitions from lowto high, the sampler 110 transitions to the regeneration phase duringwhich the input circuit 120 senses the differential input signal (e.g.,differential data signal) at the inputs 130 and 135 of the input circuit120. FIG. 3A shows an example of the voltages DINT and NDINT during theregeneration phase for the case where the input voltage INP is higherthan the input voltage INN, which may represent a bit value of one. Inthis example, the timing signal (e.g., the clock signal CLK) transitionsfrom low to high at time T1. Also, in this example, the first inputtransistor 250 and the second input transistor 255 have the samethreshold voltage 310, which is shown in FIG. 3 .

At time T1, the first switch 230 turns on, and the second switch 240 andthe third switch 245 turn off. This allows the first input transistor210 to pull down the voltage DINT based on the input voltage INP at thefirst input transistor 210, and the second input transistor 220 to pulldown the voltage NDINT based on the input voltage INN at the secondinput transistor 220. In this example, the voltage DINT is pulled down(i.e., at a faster rate than the voltage NDINT. This is because thefirst input transistor 210 is driven by a higher voltage than the secondinput transistor 220 in this example (i.e., INP>INN).

At time T2, the voltage DINT falls below the threshold voltage 310,which turns off the first input transistor 250 of the regenerationcircuit 150. The second input transistor 255 of the regeneration circuit150 is still turned on at time T2 since the voltage NDINT is still abovethe threshold voltage at time T2. Starting at time T2, the regenerativefeedback of the regeneration circuit 150 pulls up the first output 170and pulls down the second output 175 (e.g., pulls the first output 170towards the supply voltage VCC and pulls the second output 175 towardsground). The pulling up of the first output 170 and the pulling down ofthe second output 175 generates a differential output voltage at theoutputs 170 and 175 in which the output voltage OUTP is higher than theoutput voltage OUTN, which may represent a bit value of one.

FIG. 3A shows the voltages DINT and NDINT for the case where the inputvoltage INP is higher than the input voltage INN. FIG. 3B shows anexample of the voltages DINT and NDINT for the case where the inputvoltage INN is higher than the input voltage INP. In this case, thevoltage NDINT at the second output 145 of the input circuit 120 falls ata faster rate during the regeneration phase than the voltage DINT at thefirst output 140 of the input circuit 120. As a result, the voltageNDINT falls below the threshold voltage 310 before the voltage DINT,causing the second input transistor 255 to turn off before the firstinput transistor 250. When this occurs, the regenerative feedback of theregeneration circuit 150 pulls up the second output 175 and pulls downthe first output 170, resulting in a large differential output voltagein which the output voltage OUTN is higher than the output voltage OUTP,which may represent a bit decision of zero.

In both cases, it is desirable for the regeneration circuit 150 toquickly generate a large differential output voltage at the outputs 170and 175 during the regeneration phase to quickly resolve (i.e., capture)a bit value. A latch (e.g., SR latch) coupled to the outputs 170 and 175of the regeneration circuit 150 may latch the resolved bit value, asdiscussed above. When the timing signal transitions from high back tolow, the sampler 110 reenters the reset phase to reset the sampler 110for the next bit value.

As discussed above, in the example in FIG. 2B, the first switch 290 andthe second switch 295 are used to enable regenerative feedback of thefirst inverting circuit 260 and the second inverting circuit 270 duringthe regeneration phase, and disable regenerative feedback of the firstinverting circuit 260 and the second inverting circuit 270 during thereset phase. The first switch 290 and the second switch 295 disable theregenerative feedback during the reset phase by breaking thecross-coupling of the first inverting circuit 260 and the secondinverting circuit 270 when the first switch 290 and the second switch295 are turned off. However, it is to be appreciated that the presentdisclosure is not limited to this example. In general, regenerativefeedback of the first inverting circuit 260 and the second invertingcircuit 270 may be enabled or disabled using one or more switches placedat one or more locations in the regeneration circuit 150, in which theone or more switches are controlled by a timing signal (e.g., the clocksignal CLK).

In this regard, FIG. 2C shows an exemplary implementation in which theregeneration circuit 150 includes a switch 296 coupled between the upperrail 280 and the supply terminals 266 and 276 of the inverting circuits260 and 270. In this example, the first switch 290 and the second switch295 shown in FIG. 2B are omitted, in which the output 264 of the firstinverting circuit 260 is coupled to the first input transistor 250, andthe output 274 of the second inverting circuit 270 is coupled to thesecond input transistor 255. The switch 296 may be implemented with aPFET and has a control input 298 driven by the inverse of the timingsignal (e.g., inverse clock signal CLKb). In this example, the switch296 is configured to turn off during the reset phase and turn on duringthe regeneration phase. Turning off the switch 296 during the resetphase removes power to the inverting circuits 260 and 270 from the upperrail 280, which disables the regenerative feedback of the firstinverting circuit 260 and the second inverting circuit 270. It is to beappreciated that the present disclosure is not limited to the examplesshown in FIGS. 2B and 2C.

FIG. 4 shows an example in which the regeneration circuit 150 furtherincludes a pull-up circuit 405 according to certain aspects. The pull-upcircuit 405 is configured to provide an additional pull-up path duringthe regeneration phase to increase the regenerative gain of theregeneration circuit 150. The pull-up circuit 405 includes a firstpull-up transistor 410 and a second pull-up transistor 420 according tocertain aspects of the present disclosure.

In the example in FIG. 4 , the first pull-up transistor 410 isimplemented with a first PFET and the second pull-up transistor 420 isimplemented with a second PFET. The source of the first pull-uptransistor 410 is coupled to the rail 280, the drain of the firstpull-up transistor 410 is coupled to the input 262 of the firstinverting circuit 260, and the gate of the first pull-up transistor 410is coupled to the output 264 of the first inverting circuit 260. Thesource of the second pull-up transistor 420 is coupled to the rail 280,the drain of the second pull-up transistor 420 is coupled to the input272 of the second inverting circuit 270, and the gate of the secondpull-up transistor 420 is coupled to the output 274 of the secondinverting circuit 270.

Exemplary operations of the pull-up circuit 405 will now be discussedaccording to certain aspects.

When the voltage DINT falls faster than the voltage NDINT during theregeneration phase (e.g., INP>INN at the inputs 130 and 135 of the inputcircuit 120), the first input transistor 250 turns off before the secondinput transistor 255. This triggers the regenerative feedback of theregeneration circuit 150 to pull up the first output 170 and pull downthe second output 175. The pulling down of the second output 175 turnson the second pull-up transistor 420 since the gate of the secondpull-up transistor 420 is coupled to the second output 175. This causesthe second pull-up transistor 420 to pull up the input 272 of the secondinverting circuit 270 toward the supply voltage VCC on the rail 280,which helps the second inverting circuit 270 drive the output 274 of thesecond inverting circuit 270 low. Since the output 274 of the secondinverting circuit 270 is coupled to the second output 175, driving theoutput 274 of the second inverting circuit 270 low helps further pulldown the second output 175, thereby increasing the regenerative gain ofthe regeneration circuit 150. Thus, in this case, the pull-up circuit405 provides an additional pull-up path between the rail 280 and theinput 272 of the second inverting circuit 270 during the regenerationphase, which increases the regenerative gain.

When the voltage NDINT falls faster than the voltage DINT during theregeneration phase (e.g., INN>INP at the inputs 130 and 135 of the inputcircuit 120), the second input transistor 255 turns off before the firstinput transistor 250. This triggers the regenerative feedback of theregeneration circuit 150 to pull up the second output 175 and pull downthe first output 170. The pulling down of the first output 170 turns onthe first pull-up transistor 410 since the gate of the first pull-uptransistor 410 is coupled to the first output 170. This causes the firstpull-up transistor 410 to pull up the input 262 of the first invertingcircuit 260 toward the supply voltage VCC on the rail 280, which helpsthe first inverting circuit 260 drive the output 264 of the firstinverting circuit 260 low. Since the output 264 of the first invertingcircuit 260 is coupled to the first output 170, driving the output 264of the first inverting circuit 260 lower helps further pull down thefirst output 170, thereby increasing the regenerative gain of theregeneration circuit 150. Thus, in this case, the pull-up circuit 405provides an additional pull-up path between the rail 280 and the input262 of the first inverting circuit 260 during the regeneration phase,which increases the regenerative gain.

Thus, the pull-up circuit 405 is configured to provide an additionalpull-up path during the regeneration phase to increase the regenerativegain of the regeneration circuit 150. The pull-up path is between therail 280 and the input 272 of the second inverting circuit 270 when thevoltage DINT falls faster than the voltage NDINT (e.g., INP>INN), andthe pull-up path is between the rail 280 and the input 262 of the firstinverting circuit 260 when the voltage NDINT falls faster than thevoltage DINT (e.g., INN>INP).

To further increase the regenerative gain of the regeneration circuit150, a pull-down circuit may be added to the regeneration circuit 150.In this regard, FIG. 5A shows an example in which the regenerationcircuit 150 further includes a pull-down circuit 505 according tocertain aspects. The pull-down circuit 505 is configuration to providean additional pull-down path during the regeneration phase to increasethe regenerative gain of the regeneration circuit 150, which increasesthe signal strength at the outputs 170 and 175 of the regenerationcircuit 150. The pull-down circuit 505 may be used in combination withthe pull-up circuit 405 to increase regenerative gain, as discussedfurther below. The pull-down circuit 505 includes a first pull-downtransistor 510 and a second pull-down transistor 520 according tocertain aspects of the present disclosure.

In the example in FIG. 5A, the first pull-down transistor 510 isimplemented with a first NFET and the second pull-down transistor 520 isimplemented with a second NFET. The drain of the first pull-downtransistor 510 is coupled to the input 262 of the first invertingcircuit 260, the source of the first pull-down transistor 510 is coupledto the lower rail 285 (e.g., ground), and the gate of the firstpull-down transistor 510 is coupled to the input 272 of the secondinverting circuit 270 and the first output 170. The drain of the secondpull-down transistor 520 is coupled to the input 272 of the secondinverting circuit 270, the source of the second pull-down transistor 520is coupled to the lower rail 285, and the gate of the second pull-downtransistor 520 is coupled to the input 262 of the first invertingcircuit 260 and the second output 175. In other words, the firstpull-down transistor 510 and the second pull-down transistor 520 arecross-coupled.

Exemplary operations of the pull-down circuit 505 will now be discussedaccording to certain aspects.

When the voltage DINT falls faster than the voltage NDINT during theregeneration phase (e.g., INP>INN at the inputs 130 and 135 of the inputcircuit 120), the first input transistor 250 turns off before the secondinput transistor 255. This triggers the regenerative feedback of theregeneration circuit 150 to pull up the first output 170 and pull downthe second output 175. The pulling up of the first output 170 turns onthe first pull-down transistor 510 since the gate of the first pull-downtransistor 510 is coupled to the first output 170. This causes the firstpull-down transistor 510 to pull down the input 262 of the firstinverting circuit 260, which helps the first inverting circuit 260 drivethe output 264 high. Since the output 264 of the first inverting circuit260 is coupled to the first output 170, driving the output 264 of thefirst inverting circuit 260 high helps further pull up the first output170, thereby increasing regenerative gain. Thus, in this case, thepull-down circuit 505 provides an additional pull-down path between theinput 262 of the first inverting circuit 260 and the lower rail 285(e.g., ground) during the regeneration phase, which increases theregenerative gain.

When the voltage NDINT falls faster than the voltage DINT during theregeneration phase (e.g., INN>INP at the inputs 130 and 135 of the inputcircuit 120), the second input transistor 255 turns off before the firstinput transistor 250. This triggers the regenerative feedback of theregeneration circuit 150 to pull up the second output 175 and pull downthe first output 170. The pulling up of the second output 175 turns onthe second pull-down transistor 520 since the gate of the secondpull-down transistor 520 is coupled to the second output 175. Thiscauses the second pull-down transistor 520 to pull down the input 272 ofthe second inverting circuit 270, which helps the second invertingcircuit 270 drive the output 274 high. Since the output 274 of thesecond inverting circuit 270 is coupled to the second output 175,driving the output 274 of the second inverting circuit 270 high helpsfurther pull up the second output 175, thereby increasing regenerativegain. Thus, in this case, the pull-down circuit 505 provides anadditional pull-down path between the input 272 of the second invertingcircuit 270 and the lower rail 285 (e.g., ground) during theregeneration phase, which increases the regenerative gain.

Thus, the pull-down circuit 505 is configured to provide an additionalpull-down path during the regeneration phase to increase theregenerative gain of the regeneration circuit 150. The pull-down path isbetween the input 262 of the first inverting circuit 260 and the lowerrail 285 (e.g., ground) when the voltage DINT falls faster than thevoltage NDINT (e.g., INP>INN), and the pull-down path is between theinput 272 of the second inverting circuit 270 when the voltage NDINTfalls faster than the voltage DINT (e.g., INN>INP).

The pull-down circuit 505 may be used in combination with the pull-upcircuit 405 to increase the regenerative gain of the regenerationcircuit 150, which increases the signal strength at the outputs 170 and175 of the regeneration circuit 150. For example, when the voltage DINTfalls faster than the voltage NDINT (e.g., INP>INN), the pull-up circuit405 provides an additional pull-up path for pulling up the input 272 ofthe second inverting circuit 270 while the pull-down circuit 505provides an additional pull-down path for pulling down in the input 262of the first inverting circuit 260. When the voltage NDINT falls fasterthan the voltage DINT (e.g., INN>INP), the pull-up circuit 405 providesan additional pull-up path for pulling up the input 262 of the firstinverting circuit 260 while the pull-down circuit 505 provides anadditional pull-down path for pulling down in the input 272 of thesecond inverting circuit 270. Thus, in these aspects, the pull-upcircuit 405 pulls up the input of one of the inverting circuits 260 and270 and the pull-down circuit 505 pulls down the input of the other oneof the inverting circuits 260 and 270 depending on which one of thevoltages DINT and NDINT falls faster, which, in turn, depends on theinput voltages INP and INN of the input circuit 120.

Another advantage of the pull-up circuit 405 and the pull-down circuit505 is that they continue to provide regenerative gain during a firstportion of the reset phase before the input transistors 250 and 255 areturned on (i.e., before the input circuit 120 raises the voltages DINTand NDINT above the threshold voltage of the input transistors 250 and255). This is because the pull-up circuit 405 and the pull-down circuit505 continue to provide the additional pull-up path and additionalpull-down path even when the switches 290 and 295 are turned off by thetiming signal (e.g., the clock signal CLK). The continued regenerativegain during the first portion of the reset phase allows the differentialoutput voltage of the regeneration circuit 150 to continue to increasefor better resolving the corresponding bit value.

It is to be appreciated that the pull-down circuit 505 is not limited tothe exemplary implementation shown in FIG. 5A. In this regard, FIG. 5Bshows another exemplary implementation in which the gate of the firstpull-down transistor 510 is coupled to the output 264 of the firstinverting circuit 260, and the gate of the second pull-down transistor520 is coupled to the output 274 of the second inverting circuit 270.Similar to the exemplary implementation shown in FIG. 5A, the pull-downtransistors 510 and 520 in this example provide an additional pull-downpath to increase regenerative gain.

As discussed above, the pull-up circuit 405 increases regenerative gainof the regeneration circuit 150 by providing an additional pull-up pathduring the regeneration phase. The strength of the pull-up path may beincreased to further increase the regenerative gain of the regenerationcircuit 150 by increasing the sizes (e.g., channel widths) of thepull-up transistors 410 and 420. However, increasing the sizes of thepull-up transistors 410 and 420 increases the reset time of theregeneration circuit 150 resulting in a tradeoff between regenerationand reset, as discussed further below.

At the beginning of the reset phase, the input circuit 120 raises thevoltages DINT and NDINT, which are input to the input transistors 250and 255 of the regeneration circuit 150. When the voltages DINT andNDINT rise to the threshold voltage of the input transistors 250 and255, the input transistors 250 and 255 turn on to pull both inputs 262and 272 of the inverting circuits 260 and 270 low. However, one of thepull-up transistors 410 and 420 is initially on and fights the abilityof the input transistors 250 and 255 to pull both inputs 262 and 272 ofthe inverting circuits 260 and 270 low, which increases the reset time.Increasing the sizes of the pull-up transistors 410 and 420 to furtherincrease regenerative gain exacerbates this problem by making it harderfor the input transistors 250 and 255 to pull both inputs 262 and 272 ofthe inverting circuits 260 and 270 low to reset the regeneration circuit150. Thus, there is a tradeoff between regeneration and reset associatedwith the pull-up transistors 410 and 420.

To address the above, FIG. 6 shows an example in which the regenerationcircuit 150 further includes a third input transistor 610 and a fourthinput transistor 620, which mitigate the tradeoff between regenerationand reset, and increase sensitivity, as discussed further below. In thisexample, the regeneration circuit 150 also includes a third switch 630and a fourth switch 640.

The gate of the third input transistor 610 is coupled to the first input160 of the regeneration circuit 150, and therefore receives the firstvoltage DINT. The third input transistor 610 and the third switch 630are coupled in series between the rail 280 and the first output 170 ofthe regeneration circuit 150. In the example in FIG. 6 , the third inputtransistor 610 is implemented with a respective PFET, in which thesource of the third input transistor 610 is coupled to the rail 280, andthe third switch 630 is coupled between the drain of the third inputtransistor 610 and the first input transistor 250. For the example wherethe third input transistor 610 is implemented with a respective PFET,the third input transistor 610 may be configured to turn on when thefirst voltage DINT falls below VCC−Vt3 where Vt3 is the thresholdvoltage of the third input transistor 610.

The third switch 630 has a control input 635 coupled to the input 262 ofthe first inverting circuit 260. In certain aspects, the third switch630 is configured to turn on when the voltage at the control input 635is below a threshold of the third switch 630, and turn off when thevoltage at the control input 635 is above the threshold of the thirdswitch 630, as discussed further below. The third switch 630 may beimplemented with a respective PFET or another type of switch.

The gate of the fourth input transistor 620 is coupled to the secondinput 165 of the regeneration circuit 150, and therefore receives thesecond voltage NDINT. The fourth input transistor 620 and the fourthswitch 640 are coupled in series between the rail 280 and the secondoutput 175 of the regeneration circuit 150. In the example in FIG. 6 ,the fourth input transistor 620 is implemented with a respective PFET,in which the source of the fourth input transistor 620 is coupled to therail 280, and the fourth switch 640 is coupled between the drain of thefourth input transistor 620 and the second input transistor 255. For theexample where the fourth input transistor 620 is implemented with arespective PFET, the fourth input transistor 620 may be configured toturn on when the second voltage NDINT falls below VCC−Vt4 where Vt4 isthe threshold voltage of the fourth input transistor 620. In certainaspects Vt3 and Vt4 may be approximately equal.

The fourth switch 640 has a control input 645 coupled to the input 272of the second inverting circuit 270. In certain aspects, the fourthswitch 640 is configured to turn on when the voltage at the controlinput 645 is below a threshold of the fourth switch 640, and turn offwhen the voltage at the control input 645 is above the threshold of thefourth switch 640, as discussed further below. The fourth switch 640 maybe implemented with a respective PFET or another type of switch.

Exemplary operations of the exemplary regeneration circuit 150 shown inFIG. 6 will now be discussed according to certain aspects.

During the reset phase, the input circuit 120 pulls the voltages DINTand NDINT to the supply voltage VCC, as discussed above. This causes thefirst input transistor 250 and the second input transistor 255 of theregeneration circuit 150 to turn on and pull the inputs 262 and 272 ofthe inverting circuits 260 and 270 low. This also causes the third andfourth input transistors 610 and 620 of the regeneration circuit 150 toturn off since these transistors are implemented with PFETs in thisexample. Thus, in this example, the inputs 262 and 272 of the invertingcircuits 260 and 270 are reset low (e.g., approximately ground). Inaddition, both the third switch 630 and the fourth switch 640 are turnedon. This is because the input transistors 610 and 620 pull the controlinputs 635 and 645 of the third and fourth switches 630 and 640 lowduring the reset phase.

When the sampler 110 transitions to the regeneration phase, the timingsignal (e.g., the clock signal CLK) turns on the first switch 290 andthe second switch 295, enabling the regenerative feedback loop throughthe inverting circuits 260 and 270. At the start of the regenerationphase, both the first input transistor 250 and the second inputtransistor 255 are on, and both the third and fourth input transistors610 and 620 are off. In addition, both the third switch 630 and thefourth switch 640 are on.

For the case where the input voltage INP is higher than the inputvoltage INN, the first voltage DINT falls (i.e., discharges) at a fasterrate than the second voltage NDINT. This causes the first inputtransistor 250 to turn off before the second input transistor 255, andcauses the third input transistor 610 to turn on before the fourth inputtransistor 620. The turning off of the first input transistor 250triggers the regenerative feedback of the regeneration circuit 150 topull up the first output 170 and pull down the second output 175 (e.g.,pull the first output 170 towards the supply voltage VCC and pull thesecond output 175 towards ground). The turning on of the third inputtransistor 610 causes the third input transistor 610 to pull up thefirst output 170 through the third switch 630 (which is turned on).Thus, in this case, the third input transistor 610 and the third switch630 provide an additional pull-up path for pulling up the first output170, which increases regenerative gain.

The pulling up of the first output 170 turns off the fourth switch 640since the control input 645 of the fourth switch 640 is coupled to thefirst output 170. This prevents the fourth input transistor 620 frompulling up the second output 175 when the fourth input transistor 620eventually turns on (i.e., when NDINT falls below VCC-Vt4), allowing theregeneration of the regeneration circuit 150 to pull the second output175 low.

For the case where the input voltage INN is higher than the inputvoltage INP, the second voltage NDINT falls (i.e., discharges) at afaster rate than the first voltage DINT. This causes the second inputtransistor 255 to turn off before the first input transistor 250, andcauses the fourth input transistor 620 to turn on before the third inputtransistor 610. The turning off of the second input transistor 255triggers the regenerative feedback of the regeneration circuit 150 topull up the second output 175 and pull down the first output 170 (e.g.,pull the second output 175 towards the supply voltage VCC and pull thefirst output 170 towards ground). The turning on of the fourth inputtransistor 620 causes the fourth input transistor 620 to pull up thesecond output 175 through the fourth switch 640 (which is turned on).Thus, in this case, the fourth input transistor 620 and the fourthswitch 640 provide an additional pull-up path for pulling up the secondoutput 175, which increases regenerative gain.

The pulling up of the second output 175 turns off the third switch 630since the control input 635 of the third switch 630 is coupled to thesecond output 175. This prevents the third input transistor 610 frompulling up the first output 170 when the third input transistor 610eventually turns on (i.e., when DINT falls below VCC-Vt3), allowing theregeneration of the regeneration circuit 150 to pull the first output170 low.

Thus, the third input transistor 610 and the fourth input transistor 620provide an additional pull-up path during the regeneration phase toincrease the regenerative gain of the regeneration circuit 150. For thecase where the voltage DINT falls faster than the voltage NDINT (e.g.,INP>INN), the third input transistor 610 provides an additional pull-uppath between the first output 170 and the rail 280 through the thirdswitch 630. For the case where the voltage NDINT falls faster than thevoltage DINT (e.g., INN>INP), the fourth input transistor 620 providesan additional pull-up path between the second output 175 and the rail280 through the fourth switch 640.

The third input transistor 610 and the fourth input transistor 620 allowthe regeneration circuit 150 to achieve a higher regenerative gainwithout having to increase the sizes (e.g., channel widths) of the firstpull-up transistor 410 and the second pull-up transistor 420, whichmitigates the tradeoff between regeneration and reset associated withthe pull-up transistors 410 and 420. This is because the third inputtransistor 610 and the fourth input transistor 620 provide an additionalpull-up path during the regeneration phase in parallel with theadditional pull-up path provided by the pull-up transistors 410 and 420.This increases the pull-up strength of the regeneration in theregeneration circuit 150 without having to increase the sizes of thefirst pull-up transistor 410 and the second pull-up transistor 420.

In addition, the input circuit 120 turns off both the third inputtransistor 610 and the fourth input transistor 620 during the resetphase, allowing the first input transistor 250 and the second inputtransistor 255 to pull both inputs 262 and 272 of the inverting circuits260 and 270 low during the reset phase to reset the regeneration circuit150. This is because the input circuit 120 pulls the voltages DINT andNDINT to the supply voltage VCC during the reset phase, which turns offboth the third input transistor 610 and the fourth input transistor 620.Once the input circuit 120 turns off the third input transistor 610 andthe fourth input transistor 620 during the reset phase, thesetransistors no longer fight the ability of the first input transistor250 and the second input transistor 255 to pull both inputs 262 and 272of the inverting circuits 260 and 270 low during the reset phase. Thisfurther mitigates the tradeoff between regeneration and reset.

The third input transistor 610 and the fourth input transistor 620 alsoincreases the sensitivity of the sampler 110. This is because the gatesof the third input transistor 610 and the fourth input transistor 620are driven by the voltages DINT and NDINT, respectively, which aregenerated based on the sensed input voltages INP and INN, respectively.

In the example shown in FIG. 6 , the third switch 630 is coupled betweenthe third input transistor 610 and the first input transistor 250.However, it is to be appreciated that the present disclosure is notlimited to this example. For example, in some implementations, the thirdswitch 630 may be coupled between the third input transistor 610 and theupper rail 280 with the third input transistor 610 coupled between thethird switch 630 and the first input transistor 250. In general, thethird input transistor 610 and the third switch 630 are coupled inseries between the upper rail 280 and the first input transistor 250with either the third input transistor 610 or the third switch 630 ontop. Also, in some implementations, the fourth switch 640 may be coupledbetween the fourth input transistor 620 and the upper rail 280 with thefourth input transistor 620 coupled between the fourth switch 640 andthe second input transistor 255. In general, the fourth input transistor620 and the fourth switch 640 are coupled in series between the upperrail 280 and the second input transistor 255 with either the fourthinput transistor 620 or the fourth switch 640 on top.

FIG. 7 shows an exemplary implementation of the third switch 630 and thefourth switch 640. In this example, the third switch 630 is implementedwith a first PFET 710 coupled between the drain of the third inputtransistor 610 and the first input transistor 250, in which the gate ofthe first PFET 710 is coupled to the input 262 of the first invertingcircuit 260. Also, in this example, the fourth switch 640 includes asecond PFET 720 coupled between the drain of the fourth input transistor620 and the second input transistor 255, in which the gate of the secondPFET 720 is coupled to the input 272 of the second inverting circuit270. It is to be appreciated that the third switch 630 and the fourthswitch 640 are not limited to the exemplary implementation shown in FIG.7 , and that each of the third switch 630 and the fourth switch 640 maybe implemented with another type of transistor, a transmission gate, oranother type of switch.

FIG. 8 shows an example in which the first switch 290 is implementedwith a first NFET 810, and the second switch 295 is implemented with asecond NFET 820. In this example, one of the source and the drain of thefirst NFET 810 is coupled to the first input transistor 250 (e.g., thedrain of the first input transistor 250), the other one of the sourceand the drain of the first NFET 810 is coupled to the output 264 of thefirst inverting circuit 260, and the gate of the first NFET 810 iscoupled to the control input 292 to receive the timing signal (e.g., theclock signal CLK). One of the source and the drain of the second NFET820 is coupled to the second input transistor 255 (e.g., the drain ofthe second input transistor 255), the other one of the source and thedrain of the second NFET 820 is coupled to the output 274 of the secondinverting circuit 270, and the gate of the second NFET 820 is coupled tothe control input 297 to receive the timing signal (e.g., the clocksignal CLK). In this example, the first switch 290 and the second switch295 turn on when the timing signal is high and turn off when the timingsignal is low. It is to be appreciated that the first switch 290 and thesecond switch 295 are not limited to the exemplary implementation shownin FIG. 8 , and that each of the first switch 290 and the second switch295 may be implemented with another type of transistor, a transmissiongate, or another type of switch.

In the examples shown in FIGS. 4 to 8 , the regeneration circuit 150includes the first switch 290 and the second switch 295 for enabling theregenerative feedback of the inverting circuits 260 and 270 during theregeneration phase and disabling the regenerative feedback of theinverting circuits 260 and 270 during the reset phase. However, it is tobe appreciated that the present disclosure is not limited to thisexample. For example, in other implementations, the switch 296 shown inFIG. 2C may be used to enable or disable the regenerative feedback ofthe inverting circuits 260 and 270 with the first switch 290 and thesecond switch 295 omitted. In this example, the output 264 of the firstinverting circuit 260 is coupled to the first input transistor 250, andthe output 274 of the second inverting circuit 270 is coupled to thesecond input transistor 255. In general, one or more switches may beplaced at one or more locations in the regeneration circuit 150 toenable or disable the regenerative feedback of the inverting circuits260 and 270.

FIG. 9A shows an exemplary implementation of first inverting circuit 260according to certain aspects. In this example, the first invertingcircuit 260 is a complementary inverting circuit including an PFET 910and an NFET 920. The source of the PFET 910 is coupled to the firstsupply terminal 266, the drain of the PFET 910 is coupled to the output264, and the gate of the PFET 910 is coupled to the input 262. The drainof the NFET 920 is coupled to the output 264, the gate of the NFET 920is coupled to the input 262, and the source of the NFET 920 is coupledto the second supply terminal 268. It is to be appreciated that thefirst inverting circuit 260 is not limited to the example shown in FIG.9A.

FIG. 9B shows an exemplary implementation of second inverting circuit270 according to certain aspects. In this example, the second invertingcircuit 270 is a complementary inverting circuit including an PFET 930and an NFET 940. The source of the PFET 930 is coupled to the firstsupply terminal 276, the drain of the PFET 930 is coupled to the output274, and the gate of the PFET 930 is coupled to the input 272. The drainof the NFET 940 is coupled to the output 274, the gate of the NFET 940is coupled to the input 272, and the source of the NFET 940 is coupledto the second supply terminal 278. It is to be appreciated that thesecond inverting circuit 270 is not limited to the example shown in FIG.9B.

FIG. 10 shows an exemplary implementation of the first switch 230, thesecond switch 240, and the third switch 245 in the input circuit 120according to certain aspects. In this example, the first switch 230 isimplemented with an NFET 1010 in which the drain of the NFET 1010 iscoupled to the sources of the input transistors 210 and 220, the gate ofthe NFET 1010 is coupled to the control input 235, and the source of theNFET 1010 is coupled to the lower rail 285 (e.g., ground). The secondswitch 240 is implemented with a first PFET 1015 in which the source ofthe first PFET 1015 is coupled to the upper rail 280, the gate of thefirst PFET 1015 is coupled to the control input 242, and the drain ofthe first PFET 1015 is coupled to the drain of the first inputtransistor 210. The third switch 245 is implemented with a second PFET1020 in which the source of the second PFET 1020 is coupled to the upperrail 280, the gate of the second PFET 1020 is coupled to the controlinput 247, and the drain of the second PFET 1020 is coupled to the drainof the second input transistor 220. In this example, the first switch230 turns on when the timing signal is high and turns off when thetiming signal is low. Also, in this example, the second switch 240 andthe third switch 24 turn on when the timing signal is low and turn offwhen the timing signal is high. It is to be appreciated that the firstswitch 230, the second switch 240, and the third switch 245 are notlimited to the exemplary implementation shown in FIG. 10 .

FIG. 11 shows an example of a system 1105 in which aspects of thepresent disclosure may be used. In this example, the system 1105includes a first chip 1110 and a second chip 1115 in which SerDes may beused for communication between the first chip 1110 and the second chip1115. The first chip 1110 includes a serializer 1120, a driver 1130, afirst output pin 1140, and a second output pin 1142. The second chip1115 includes a first receive pin 1150, a second receive pin 1152, areceiver 1160, the sampler 110, a latch 1170, and a deserializer 1180.

In this example, the first chip 1110 and the second chip 1115 arecoupled via a differential serial link including a first line 1144 and asecond line 1146. The first line 1144 is coupled between the firstoutput pin 1140 and the first receive pin 1150, and the second line 1146is coupled between the second output pin 1142 and the second receive pin1152. The first line 1144 and the second line 1146 may each beimplemented with a metal line on a substrate (e.g., a printed circuitboard), a wire, etc.

On the first chip 1110, the serializer 1120 is configured to receiveparallel data streams (e.g., from a processor on the first chip 1110)and convert the parallel data streams into a serial data stream, whichis output at an output 1125 of the serializer 1120. The driver 1130 hasan input 1132 coupled to the output 1125 of the serializer 1120, a firstoutput 1134 coupled to the first output pin 1140, and a second output1136 coupled to the second output pin 1142. The driver 1130 isconfigured to receive the serial data stream, convert the serial datastream into a differential signal, and drive the first line 1144 and thesecond line 1146 of the differential seral link with the differentialdata signal to transmit the differential signal to the second chip 1115.It is to be appreciated that the first chip 1110 may include additionalcomponents not shown in FIG. 11 (e.g., impedance matching networkcoupled to the output pins 1140 and 1142, a pre-driver coupled betweenthe serializer 1120 and the driver 1130, etc.).

On the second chip 1115, the receiver 1160 has a first input 1162coupled to the first receive pin 1150, a second input 1164 coupled tothe second receive pin 1152, a first output 1166 coupled to the firstinput 130 of the sampler 110, and a second output 1168 coupled to thesecond input 135 of the sampler 110. The receiver 1160 may include atleast one of an amplifier and an equalizer (e.g., to compensate forfrequency-dependent signal attenuation between the first chip 1110 andthe second chip 1115). The sampler 110 receives the differential signalfrom the receiver 1160 and makes bit decisions based on the differentialsignal, as discussed above.

In the example in FIG. 11 , the first output 170 of the sampler 110 iscoupled to a first input 1172 of the latch 1170, and the second output175 of the sampler 110 is coupled to a second input 1174 of the latch1170. The latch 1170 has an output 1176 coupled to an input 1182 of thedeserializer 1180. The latch 1170 is configured to latch bit decisionsfrom the sampler 110 and output the corresponding bits to thedeserializer 1180. The deserializer 1180 is configured to convert thebits into parallel data streams, which may be output to one or morecomponents (not shown) on the second chip 1115 for further processing.It is to be appreciated that the second chip 1115 may include additionalcomponents not shown in FIG. 11 (e.g., impedance matching networkcoupled to the receive pins 1150 and 1152, a clock recovery circuit,etc.).

In the example in FIG. 11 , the second chip 1115 also includes a timingsignal circuit 1190 configured to generate the timing signal (e.g.,clock signal CLK) for the sampler 110 and output the timing signal atoutput 1194. The output 1194 may be coupled to the control inputs of theswitches 230, 240, and 245 in the input circuit 120 and the controlinputs of the switches 290 and 295 in the regeneration circuit 150 ofthe sampler 110.

In certain aspects, the timing signal circuit 1190 may recover thetiming signal (e.g., clock signal CLK) based on the bit decisions of thesampler 110 using clock data recovery. The input 1192 of the timingsignal circuit 1190 may be coupled to the output of the latch 1170(shown in the example in FIG. 11 ) or may be coupled to one or bothoutputs 170 and 175 of the sampler 110 to receive the bit decisions.

In certain aspects, the timing signal circuit 1190 may include a clockgenerator which may include a phase locked loop (PLL), a delay lockedloop (DLL), an oscillator, or any combination thereof to generate thetiming signal (e.g., clock signal CLK). It is to be appreciated that thetiming signal circuit 1190 may be implemented using various types ofclock generators.

FIG. 12 illustrates a method 1200 of operating a regeneration circuit ofa sampler according to certain aspects. The regeneration circuit (e.g.,regeneration circuit 150) includes a first inverting circuit (e.g.,first inverting circuit 260) having an input and an output, a secondinverting circuit (e.g., second inverting circuit 270) having an inputand an output, a first transistor (e.g., first input transistor 250)coupled to the input of the second inverting circuit, a secondtransistor (e.g., second input transistor 255) coupled to the input ofthe first inverting circuit, a third transistor (e.g., third inputtransistor 610), and a fourth transistor (e.g., fourth input transistor620).

At block 1210, during a reset phase, a regenerative feedback of thefirst inverting circuit and the second inverting circuit is disabled.For example, disabling the regenerative feedback of the first invertingcircuit and the second inverting circuit may include decoupling theoutput of the first inverting circuit from the first transistor, anddecoupling the output of the second inverting circuit from the secondtransistor. For example, the output of the first inverting circuit maybe decoupled from the first transistor by turning off the first switch290 (e.g., using the timing signal), and the output of the secondinverting circuit may be decoupled from the second transistor by turningoff the second switch 295 (e.g., using the timing signal). In anotherexample, disabling the regenerative feedback of the first invertingcircuit and the second inverting circuit may include turning off theswitch 296 shown in FIG. 2C.

At block 1220, during a regeneration phase, the regenerative feedback ofthe first inverting circuit and the second inverting circuit is enabled.For example, enabling the regenerative feedback of the first invertingcircuit and the second inverting circuit may include coupling the outputof the first inverting circuit to the first transistor, and coupling theoutput of the second inverting circuit to the second transistor. Forexample, the output of the first inverting circuit may be coupled to thefirst transistor by turning on the first switch 290 (e.g., using thetiming signal), and the output of the second inverting circuit may becoupled to the second transistor by turning on the second switch 295(e.g., using the timing signal). In another example, enabling theregenerative feedback of the first inverting circuit and the secondinverting circuit may include turning on the switch 296 shown in FIG.2C.

At block 1230, during the regeneration phase, a gate of the firsttransistor and a gate of the third transistor are driven with a firstvoltage. For example, the input circuit 120 may drive the gate of thefirst transistor and the gate of the third transistor with the firstvoltage DINT.

At block 1240, during the regeneration phase, a gate of the secondtransistor and a gate of the fourth transistor are driven with a secondvoltage. For example, the input circuit 120 may drive the gate of thesecond transistor and the gate of the fourth transistor with the secondvoltage NDINT.

At block 1250, during the regeneration phase, the third transistor iscoupled to the output of the first inverting circuit or the fourthtransistor is coupled to the output of the second inverting circuit. Forexample, the third switch 630 may couple the third transistor to theoutput of the first inverting circuit or the fourth switch 640 maycouple the fourth transistor to the output of the second invertingcircuit.

In certain aspects, during the regeneration phase, the first voltagefalls at a first rate, the second voltage falls at a second rate, andthe first rate is different from the second rate. For example, the firstrate may be based on a first input signal (e.g., INP) to the sampler,and the second rate may be based on a second input signal (e.g., INN) tothe sampler. In one example, the first input transistor 210 of the inputcircuit 120 may discharge the first node 222 based on the first inputsignal INP causing the first voltage DINT to fall at the first rate, andthe second input transistor 220 of the input circuit 120 may dischargethe second node 224 based on the second input signal INN causing thesecond voltage NDINT to fall at the second rate. In this example, thegate of the first input transistor 210 may be driven by the first inputsignal INP, and the gate of the second input transistor 220 may bedriven by the second input signal INN.

In certain aspects, the first rate is greater than the second rate ifthe first input signal is greater than the second input signal (e.g.,INP>INN), and the second rate is greater than the first rate if thesecond input signal is greater than the first input signal (e.g.,INN>INP).

In certain aspects, coupling the third transistor to the output of thefirst inverting circuit or coupling the fourth transistor to the outputof the second inverting circuit includes coupling the third transistorto the output of the first inverting circuit based on a voltage at theinput of the first inverting circuit or coupling the fourth transistorto the output of the second inverting circuit based on a voltage at theinput of the second inverting circuit. For example, the control input635 of the third switch 630 may be coupled to the input 262 of the firstinverting circuit 260, and the control input 645 of the fourth switch640 may be coupled to the input 272 of the second inverting circuit 270.

The method 1200 may also include, during the reset phase, pulling up thefirst voltage and the second voltage to a supply voltage. For example,the first voltage DINT and the second voltage NDINT may be pulled up tothe supply voltage VCC by turning on the second switch 240 and the thirdswitch 245 of the input circuit 120 in the reset phase.

Implementation examples are described in the following numbered clauses:

1. A regeneration circuit, comprising:

a first inverting circuit having an input and an output;

a second inverting circuit having an input and an output;

a first transistor coupled to the input of the second inverting circuit,wherein a gate of the first transistor is coupled to a first input;

a second transistor coupled to the input of the first inverting circuit,wherein a gate of the second transistor is coupled to a second input;

a third transistor, wherein a gate of the third transistor is coupled tothe first input;

a fourth transistor, wherein a gate of the fourth transistor is coupledto the second input;

a first switch, wherein the first switch and the third transistor arecoupled in series between a first rail and the first transistor; and

a second switch, wherein the second switch and the fourth transistor arecoupled in series between the first rail and the second transistor.

2. The regeneration circuit of clause 1, wherein:

the first switch is coupled between a drain of the third transistor anda drain of the first transistor; and

the second switch is coupled between a drain of the fourth transistorand a drain of the second transistor.

3. The regeneration circuit of clause 2, wherein:

a source of the third transistor is coupled to the first rail;

a source of the fourth transistor is coupled to the first rail;

a source of the first transistor is coupled to a second rail; and

a source of the second transistor is coupled to the second rail.

4. The regeneration circuit of clause 3, wherein the second rail iscoupled to a ground.

5. The regeneration circuit of any one of clauses 1 to 4, wherein:

the first transistor comprises a first n-type field effect transistor(NFET);

the second transistor comprises a second NFET;

the third transistor comprises a first p-type field effect transistor(PFET); and

the fourth transistor comprises a second PFET.

6. The regeneration circuit any one of clauses 1 to 5, wherein:

the first switch has a control input coupled to the input of the firstinverting circuit; and

the second switch has a control input coupled to the input of the secondinverting circuit.

7. The regeneration circuit of clause 6, wherein:

the first switch comprises a first p-type field effect transistor (PFET)having a gate coupled to the input of the first inverting circuit; and

the second switch comprises a second PFET having a gate coupled to theinput of the second inverting circuit.

8. The regeneration circuit of any one of clauses 1 to 7, furthercomprising:

a third switch coupled between the first transistor and the output ofthe first inverting circuit; and

a fourth switch coupled between the second transistor and the output ofthe second inverting circuit.

9. The regeneration circuit of clause 8, wherein:

the third switch has a control input configured to receive a timingsignal; and

the fourth switch has a control input configured to receive the timingsignal.

10. The regeneration circuit of clause 9, wherein the timing signalcomprises a clock signal.

11. A regeneration circuit, comprising:

a first inverting circuit having an input and an output;

a second inverting circuit having an input and an output;

a first transistor coupled to the input of the second inverting circuit,wherein a gate of the first transistor is coupled to a first input;

a second transistor coupled to the input of the first inverting circuit,wherein a gate of the second transistor is coupled to a second input;

a pull-up circuit coupled to the input of the first inverting circuitand the input of the second inverting circuit; and

a pull-down circuit coupled to the input of the first inverting circuitand the input of the second inverting circuit.

12. The regeneration circuit of clause 11, wherein the pull-up circuitcomprises:

a third transistor coupled between the input of the first invertingcircuit and a rail, wherein a gate of the third transistor is coupled tothe output of the first inverting circuit; and

a fourth transistor coupled between the input of the second invertingcircuit and the rail, wherein a gate of the fourth transistor is coupledto the output of the second inverting circuit.

13. The regeneration circuit of clause 12, wherein:

the third transistor comprises a first p-type field effect transistor(PFET); and

the fourth transistor comprises a second PFET.

14. The regeneration circuit of clause 13, wherein:

a source of the first PFET is coupled to the rail and a drain of thefirst PFET is coupled to the input of the first inverting circuit; and

a source of the second PFET is coupled to the rail and a drain of thesecond PFET is coupled to the input of the second inverting circuit.

15. The regeneration circuit of clause 11, wherein the pull-down circuitcomprises:

a third transistor coupled between the input of the first invertingcircuit and a rail, wherein a gate of the third transistor is coupled tothe input of the second inverting circuit or the output of the firstinverting circuit; and

a fourth transistor coupled between the input of the second invertingcircuit and the rail, wherein a gate of the fourth transistor is coupledto the input of the first inverting circuit or the output of the secondinverting circuit.

16. The regeneration circuit of clause 15, wherein:

the third transistor comprises a first n-type field effect transistor(NFET); and

the fourth transistor comprises a second NFET.

17. The regeneration circuit of clause 16, wherein:

a drain of the first NFET is coupled to the input of the first invertingcircuit and a source of the first NFET is coupled to the rail; and

a drain of the second NFET is coupled to the input of the secondinverting circuit and a source of the second NFET is coupled to therail.

18. The regeneration circuit of any one of clauses 15 to 17, wherein therail is coupled to ground.

19. The regeneration circuit of any one of clauses 11 to 18, furthercomprising:

a first switch coupled between the first transistor and the output ofthe first inverting circuit; and

a second switch coupled between the second transistor and the output ofthe second inverting circuit.

20. The regeneration circuit of clause 19, wherein:

the first switch has a control input configured to receive a timingsignal; and

the second switch has a control input configured to receive the timingsignal.

21. A method of operating a regeneration circuit of a sampler, whereinthe regeneration circuit includes a first inverting circuit having aninput and an output, a second inverting circuit having an input and anoutput, a first transistor coupled to the input of the second invertingcircuit, a second transistor coupled to the input of the first invertingcircuit, a third transistor, and a fourth transistor, the methodcomprising:

during a reset phase,

disabling a regenerative feedback of the first inverting circuit and thesecond inverting circuit;

during a regeneration phase,

enabling the regenerative feedback of the first inverting circuit andthe second inverting circuit;

driving a gate of the first transistor and a gate of the thirdtransistor with a first voltage;

driving a gate of the second transistor and a gate of the fourthtransistor with a second voltage; and

coupling the third transistor to the output of the first invertingcircuit or coupling the fourth transistor to the output of the secondinverting circuit.

22. The method of clause 21, during the regeneration phase, the firstvoltage falls at a first rate, the second voltage falls at a secondrate, and the first rate is different from the second rate.

23. The method of clause 22, wherein the first rate is based on a firstinput signal to the sampler, and the second rate is based on a secondinput signal to the sampler.

24. The method of clause 23, wherein the first rate is greater than thesecond rate if the first input signal is greater than the second inputsignal, and the second rate is greater than the first rate if the secondinput signal is greater than the first input signal.

25. The method of any one of clauses 22 to 24, wherein coupling thethird transistor to the output of the first inverting circuit orcoupling the fourth transistor to the output of the second invertingcircuit comprises:

coupling the third transistor to the output of the first invertingcircuit if the first rate is greater than the second rate; and

coupling the fourth transistor to the output of the second invertingcircuit if the second rate is greater than the first rate.

26. The method of any one of clauses 22 to 25, wherein coupling thethird transistor to the output of the first inverting circuit orcoupling the fourth transistor to the output of the second invertingcircuit comprises:

coupling the third transistor to the output of the first invertingcircuit based on a voltage at the input of the first inverting circuitor coupling the fourth transistor to the output of the second invertingcircuit based on a voltage at the input of the second inverting circuit.

27. The method of any one of clauses 21 to 26, further comprising,during the reset phase, pulling up the first voltage and the secondvoltage to a supply voltage.

28. The method of any one of clauses 21 to 27, wherein:

the first transistor comprises a first n-type field effect transistor(NFET);

the second transistor comprises a second NFET;

the third transistor comprises a first p-type field effect transistor(PFET); and

the fourth transistor comprises a second PFET.

29. The method of any one of clauses 21 to 28, wherein:

disabling the regenerative feedback of the first inverting circuit andthe second inverting circuit comprises:

decoupling the output of the first inverting circuit from the firsttransistor; and

decoupling the output of the second inverting circuit from the secondtransistor;

and

enabling the regenerative feedback of the first inverting circuit andthe second inverting circuit comprises:

coupling the output of the first inverting circuit to the firsttransistor; and

coupling the output of the second inverting circuit to the secondtransistor.

30. The regeneration circuit of any one of clauses 12 to 14, wherein thepull-down circuit comprises:

a fifth transistor coupled between the input of the first invertingcircuit and a second rail, wherein a gate of the fifth transistor iscoupled to the input of the second inverting circuit or the output ofthe first inverting circuit; and

a sixth transistor coupled between the input of the second invertingcircuit and the second rail, wherein a gate of the sixth transistor iscoupled to the input of the first inverting circuit or the output of thesecond inverting circuit.

31. The regeneration circuit of clause 30, wherein:

the fifth transistor comprises a first n-type field effect transistor(NFET); and

the sixth transistor comprises a second NFET.

32. The regeneration circuit of clause 31, wherein:

a drain of the first NFET is coupled to the input of the first invertingcircuit and a source of the first NFET is coupled to the rail; and

a drain of the second NFET is coupled to the input of the secondinverting circuit and a source of the second NFET is coupled to therail.

33. The regeneration circuit of any one of clauses 30 to 32, wherein thesecond rail is coupled to ground.

It is to be appreciated that the present disclosure is not limited tothe exemplary terminology used above to describe aspects of the presentdisclosure.

Any reference to an element herein using a designation such as “first,”“second,” and so forth does not generally limit the quantity or order ofthose elements. Rather, these designations are used herein as aconvenient way of distinguishing between two or more elements orinstances of an element. Thus, a reference to first and second elementsdoes not mean that only two elements can be employed, or that the firstelement must precede the second element. Further, it is to beappreciated that the designations “first,” “second,” and so forth in thewritten description do not necessary match the designations “first,”“second,” and so forth in the claims.

Within the present disclosure, the word “exemplary” is used to mean“serving as an example, instance, or illustration.” Any implementationor aspect described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other aspects of thedisclosure. Likewise, the term “aspects” does not require that allaspects of the disclosure include the discussed feature, advantage ormode of operation. The term “approximately”, as used herein with respectto a stated value or a property, is intended to indicate being within10% of the stated value or property.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples described herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. A regeneration circuit, comprising: a firstinverting circuit having an input and an output; a second invertingcircuit having an input and an output; a first transistor coupled to theinput of the second inverting circuit, wherein a gate of the firsttransistor is coupled to a first input; a second transistor coupled tothe input of the first inverting circuit, wherein a gate of the secondtransistor is coupled to a second input; a third transistor, wherein agate of the third transistor is coupled to the first input; a fourthtransistor, wherein a gate of the fourth transistor is coupled to thesecond input; a first switch, wherein the first switch and the thirdtransistor are coupled in series between a first rail and the firsttransistor; and a second switch, wherein the second switch and thefourth transistor are coupled in series between the first rail and thesecond transistor.
 2. The regeneration circuit of claim 1, wherein: thefirst switch is coupled between a drain of the third transistor and adrain of the first transistor; and the second switch is coupled betweena drain of the fourth transistor and a drain of the second transistor.3. The regeneration circuit of claim 2, wherein: a source of the thirdtransistor is coupled to the first rail; a source of the fourthtransistor is coupled to the first rail; a source of the firsttransistor is coupled to a second rail; and a source of the secondtransistor is coupled to the second rail.
 4. The regeneration circuit ofclaim 3, wherein the second rail is coupled to a ground.
 5. Theregeneration circuit of claim 1, wherein: the first transistor comprisesa first n-type field effect transistor (NFET); the second transistorcomprises a second NFET; the third transistor comprises a first p-typefield effect transistor (PFET); and the fourth transistor comprises asecond PFET.
 6. The regeneration circuit of claim 1, wherein: the firstswitch has a control input coupled to the input of the first invertingcircuit; and the second switch has a control input coupled to the inputof the second inverting circuit.
 7. The regeneration circuit of claim 6,wherein: the first switch comprises a first p-type field effecttransistor (PFET) having a gate coupled to the input of the firstinverting circuit; and the second switch comprises a second PFET havinga gate coupled to the input of the second inverting circuit.
 8. Theregeneration circuit of claim 1, further comprising: a third switchcoupled between the first transistor and the output of the firstinverting circuit; and a fourth switch coupled between the secondtransistor and the output of the second inverting circuit.
 9. Theregeneration circuit of claim 8, wherein: the third switch has a controlinput configured to receive a timing signal; and the fourth switch has acontrol input configured to receive the timing signal.
 10. Theregeneration circuit of claim 9, wherein the timing signal comprises aclock signal.
 11. A regeneration circuit, comprising: a first invertingcircuit having an input and an output; a second inverting circuit havingan input and an output; a first transistor coupled to the input of thesecond inverting circuit, wherein a gate of the first transistor iscoupled to a first input; a second transistor coupled to the input ofthe first inverting circuit, wherein a gate of the second transistor iscoupled to a second input; a pull-up circuit coupled to the input of thefirst inverting circuit and the input of the second inverting circuit;and a pull-down circuit coupled to the input of the first invertingcircuit and the input of the second inverting circuit.
 12. Theregeneration circuit of claim 11, wherein the pull-up circuit comprises:a third transistor coupled between the input of the first invertingcircuit and a rail, wherein a gate of the third transistor is coupled tothe output of the first inverting circuit; and a fourth transistorcoupled between the input of the second inverting circuit and the rail,wherein a gate of the fourth transistor is coupled to the output of thesecond inverting circuit.
 13. The regeneration circuit of claim 12,wherein: the third transistor comprises a first p-type field effecttransistor (PFET); and the fourth transistor comprises a second PFET.14. The regeneration circuit of claim 13, wherein: a source of the firstPFET is coupled to the rail and a drain of the first PFET is coupled tothe input of the first inverting circuit; and a source of the secondPFET is coupled to the rail and a drain of the second PFET is coupled tothe input of the second inverting circuit.
 15. The regeneration circuitof claim 11, wherein the pull-down circuit comprises: a third transistorcoupled between the input of the first inverting circuit and a rail,wherein a gate of the third transistor is coupled to the input of thesecond inverting circuit or the output of the first inverting circuit;and a fourth transistor coupled between the input of the secondinverting circuit and the rail, wherein a gate of the fourth transistoris coupled to the input of the first inverting circuit or the output ofthe second inverting circuit.
 16. The regeneration circuit of claim 15,wherein: the third transistor comprises a first n-type field effecttransistor (NFET); and the fourth transistor comprises a second NFET.17. The regeneration circuit of claim 16, wherein: a drain of the firstNFET is coupled to the input of the first inverting circuit and a sourceof the first NFET is coupled to the rail; and a drain of the second NFETis coupled to the input of the second inverting circuit and a source ofthe second NFET is coupled to the rail.
 18. The regeneration circuit ofclaim 15, wherein the rail is coupled to ground.
 19. The regenerationcircuit of claim 11, further comprising: a first switch coupled betweenthe first transistor and the output of the first inverting circuit; anda second switch coupled between the second transistor and the output ofthe second inverting circuit.
 20. The regeneration circuit of claim 19,wherein: the first switch has a control input configured to receive atiming signal; and the second switch has a control input configured toreceive the timing signal.
 21. A method of operating a regenerationcircuit of a sampler, wherein the regeneration circuit includes a firstinverting circuit having an input and an output, a second invertingcircuit having an input and an output, a first transistor coupled to theinput of the second inverting circuit, a second transistor coupled tothe input of the first inverting circuit, a third transistor, and afourth transistor, the method comprising: during a reset phase,disabling a regenerative feedback of the first inverting circuit and thesecond inverting circuit; during a regeneration phase, enabling theregenerative feedback of the first inverting circuit and the secondinverting circuit; driving a gate of the first transistor and a gate ofthe third transistor with a first voltage; driving a gate of the secondtransistor and a gate of the fourth transistor with a second voltage;and coupling the third transistor to the output of the first invertingcircuit or coupling the fourth transistor to the output of the secondinverting circuit.
 22. The method of claim 21, during the regenerationphase, the first voltage falls at a first rate, the second voltage fallsat a second rate, and the first rate is different from the second rate.23. The method of claim 22, wherein the first rate is based on a firstinput signal to the sampler, and the second rate is based on a secondinput signal to the sampler.
 24. The method of claim 23, wherein thefirst rate is greater than the second rate if the first input signal isgreater than the second input signal, and the second rate is greaterthan the first rate if the second input signal is greater than the firstinput signal.
 25. The method of claim 22, wherein coupling the thirdtransistor to the output of the first inverting circuit or coupling thefourth transistor to the output of the second inverting circuitcomprises: coupling the third transistor to the output of the firstinverting circuit if the first rate is greater than the second rate; andcoupling the fourth transistor to the output of the second invertingcircuit if the second rate is greater than the first rate.
 26. Themethod of claim 22, wherein coupling the third transistor to the outputof the first inverting circuit or coupling the fourth transistor to theoutput of the second inverting circuit comprises: coupling the thirdtransistor to the output of the first inverting circuit based on avoltage at the input of the first inverting circuit or coupling thefourth transistor to the output of the second inverting circuit based ona voltage at the input of the second inverting circuit.
 27. The methodof claim 21, further comprising, during the reset phase, pulling up thefirst voltage and the second voltage to a supply voltage.
 28. The methodof claim 21, wherein: the first transistor comprises a first n-typefield effect transistor (NFET); the second transistor comprises a secondNFET; the third transistor comprises a first p-type field effecttransistor (PFET); and the fourth transistor comprises a second PFET.29. The method of claim 21, wherein: disabling the regenerative feedbackof the first inverting circuit and the second inverting circuitcomprises: decoupling the output of the first inverting circuit from thefirst transistor; and decoupling the output of the second invertingcircuit from the second transistor; and enabling the regenerativefeedback of the first inverting circuit and the second inverting circuitcomprises: coupling the output of the first inverting circuit to thefirst transistor; and coupling the output of the second invertingcircuit to the second transistor.